Humidity and condensate removal
Biogas is often generated at high moisture environment, and therefore large amount of water vapor is carried within biogas. As the biogas cools down along the pipeline, condensate will build up at the lowest point, which will cause blockage and dangerous system over-pressure. If the moisture is not reduced before the biogas engine, the condensate will build up in the combustion chamber and cause severe damage to the engine.
To remove the condensate, the biogas piping needs to be designed with slope and condensate collection tank/pot needs to be placed at the lowest points. Very often the gravel filter immediately after the digester can remove large amount of condensate as well.
To reduce the relative humidity, which is the water vapor in biogas, cooler dryer is commonly used. The amount of water vapor in 1 cu. meter biogas is a function of temperature as per the graph below. by reducing the biogas temperature from 37 to 5 degree C, the water vapor is reduced from 0.044 to 0.007 kg/m3. 84% of water vapor can be removed as condensate. A biogas compressor can often heat the biogas up to 30 degree C, and the relative humidity is reduced to around 30%, which eliminates the risk of condensation. In the meanwhile, by cooling the biogas, some non-methane hydrocarbons, commonly found in landfill gas, can be removed at the same time.
Do remember that the condensate collected needs to be drained from time to time. If the condensate is clean, automatic drain valve can be used.